Hey everyone, I know this may not help terribly much, but I was having the exact same problem as you all and my game suddenly fixed itself. I don't know what I did or how I did it, all I can say is the game "snapped to" on a second playthrough as I recruited Aloth in Gilded Vale. After that, the SFX began to work properly and the delays on portrait selection and inventory disappeared. Even the load times between areas got shorter. Again, no idea how this happened, but there must be something I did or had happen in-game to resolve this issue.